In industrial installations utilizing screwed connection members, traction is generally applied to said members with the aid of a tensioning device for the purpose of holding them in a prestressed state, and while this traction is applied, a nut holding the connection member in position is screwed on or off.
This is in particular the case with pressure vessels used in industry, especially the nuclear, chemical or petrochemical industries, wehere it is necessary to screw or unscrew a clamping and holding nut onto or off each connection member consisting, for example, of a bolt, while applying traction with the aid of an appropriate device to all said connection members with the aid of a tensioning nut also screwed onto each connection member.
This is also the case in the automobile and aeronautical industries, in which numerous screwed connection members are used.
These connection members are generally used in fairly large numbers and relatively close to one another, so that on every intervention it is necessary to screw on or off both the tensioning nut and the holding nut on each connection member.
These operations of successively screwing or unscrewing the different nuts are lengthy and delicate, and can only be carried out automatically.